Alloy, in particular for a bearing coating

ABSTRACT

The invention relates to an alloy, in particular for an anti-friction coating, comprising elements which form a matrix ( 2 ) and at least a soft phase ( 3 ) and/or a hard phase ( 5 ), which soft phase elements and/or hard phase elements form a solid solution or a bond with the matrix element. The soft phase ( 3 ) and/or hard phase ( 5 ) is dispersed in the matrix ( 2 ) and the solid solution or bond is formed only in the region of the phase boundary ( 4 ) of the matrix ( 2 ) with the soft phase ( 3 ) and/or with the hard phase ( 5 ).

The invention relates to an alloy, in particular for an anti-frictioncoating, comprising elements which form a matrix and at least a softphase and/or a hard phase, which soft phase elements and/or hard phaseelements produce a solid solution or bond with the matrix element, ananti-friction coating, in particular a bearing anti-friction coatingmade from the alloy, a composite material comprising at least a firstperipheral coating and a second peripheral coating disposed opposite it,for example a protective coating of steel, in particular foranti-friction bearings or thrust washers, a method of producing thecomposite material and the use of the alloy to produce an anti-frictioncoating for an anti-friction bearing or a thrust washer or for directlycoating components subjected to friction stress.

Technical progress made in the engine construction industry has meantthat increasingly tough requirements are being placed on many aspects ofanti-friction elements, such as plain bearings or thrust washers orsliding bushes for example. The anti-friction element or itsanti-friction coating should be soft enough to enable it to adapt wellto faults of the cooperating anti-friction element caused by productionon the one hand, but the anti-friction coating should be sufficientlyhard or have a high enough strength to exhibit good durability orbearing capacity during operation at high speeds and when subjected tovibrations or high mechanical stress, on the other hand. The propertieswhich can be achieved in these anti-friction coatings and bearingsalways mean having to strike a compromise. If the emphasis is on goodrunning-in or resistance to galling, the anti-friction coating itself isusually only able to withstand low mechanical stress because the forcesto which the shaft or the bearing is exposed are transmitted as a wholeand exclusively by the soft anti-friction coating which is thereforesusceptible to wear at an early stage. If, on the other hand, elementsare provided which are capable of withstanding such abrasion, they areso at the expensive of reduced ability of the coating to adapt.

In the case of standard coatings made by hot metal processingtechniques, such as disclosed in patent specifications WO 97/22725 A orDE 39 06 402 C2, an attempt is made to combine these intrinsicallycontradictory property profiles by alloying an element which forms thematrix of the material, elements which form the soft phases, such aslead, tin, zinc or bismuth, for example, so that the coating is able toadapt and embed pieces abraded from the parts to be supported, e.g.shafts. In order to increase the strength and bearing capacity, otherelements are incorporated in the alloy which form a hard phase, forexample inter-metallic compounds or mixed crystals. Depending on thecontent of the different elements, the emphasis will therefore be ongood ability to embed or good resistance to galling or high bearingcapacity.

Also quite common are anti-friction elements made from copper-basedmaterials, for example, which as a rule have a high grinding resistancedue to elements forming soft phases, such as lead. Due to the fact thatit does not mix or as a result of the gaps which occur when copper andlead are mixed, the lead separates and disperses in the copper matrixand is responsible for the good tribological properties of thismaterial.

Thermally sprayed coatings for runner blades are known from patentspecification DE 198 09 721 A1, and the coating has a higher degree ofhardness than the underlying metal base in order to increase resistanceto abrasion. Amongst the coating materials mentioned are alloys with abase of Ni, Co, Fe, cermets or hard metals.

Patent specification EP 0 911 425 A1 describes a method of spraying coldgas as a means of coating substrate materials. Amongst others, nitrogen,argon, neon, xenon or carbon dioxide are mentioned as a process gas.Overall, the intention is to improve the quality of the coating on thebasis of an appropriate temperature, pressure and particle velocity.

The objective of the invention is to propose an alloy and ananti-friction coating for an anti-friction element, which, in additionto exhibiting good run-in properties, also has a high resistance towear.

This objective is achieved by the invention, in each case independently,by means of an alloy of the type described above, in which the softphase and/or the hard phase is dispersed in the matrix and the solidsolution or bond is formed only in the region of the phase boundary ofthe matrix with the soft phase and/or with the hard phase, ananti-friction coating formed therefrom, a composite material comprisinga first peripheral coating made from the anti-friction coating proposedby the invention as well as a method, whereby, using a cold gas sprayingprocess, an alloy as proposed by the invention can be produced as afirst peripheral coating. The advantage of this approach is that it isnow possible to produce an alloy and an anti-friction coating foranti-friction elements which can not be produced using the molten metalprocesses known from the prior art or with other thermal sprayingprocesses. The fact that the particles of the initial powder are notmelted advantageously enables anti-friction coatings containing alloyelements to be produced, which can not be combined using standardproduction or melting methods to obtain the desired properties, such ashigh resistance to wear or high bearing capacity and good run-inproperties, because the elements are not present as a soft phase but inthe form of mixed crystals or compounds. The alloy or the combination ofalloy elements which form a stable phase or phase mixtures in the formof mixed crystals or inter-metallic compounds based on the correspondingphase diagram for a selected composition using metallurgical techniquesbased on melting, in other words which do not separate, can be producedby the present invention in the form of a virtually separating alloysystem. The advantage of the alloy proposed by the invention is that thesolid solution or bond occurs only in the region of the phase boundariesas a result of which both soft phases and hard phases are essentiallydispersed in the matrix. This means that elements can also be used assoft phases and can therefore be employed as a means of impartinggalling resistance properties to the bearing, which, if produced bycasting or sintering or similar methods, would be present in the matrixas mixed crystals and would thus tend to increase strength instead ofbeing available as soft phases. Likewise, the hard particles or hardphases may be dispersed in the material in their original composition,the particular advantage of which is that they can increase the wearresistance of the coating and will not react with the matrix or otherelements as is the case with conventionally produced bearings, forexample due to the formation of inter-metallic phases. Another advantageis that during operation, the coating undergoes a sort of heat treatmentin areas where the anti-friction coating is particularly subjected toloads due to the increases in temperature which occur locally, as aresult of which a slow phase transformation takes place in these areasand the alloy moves close to thermodynamic equilibrium. The materialhardens in these areas. As a result, the anti-friction coating is harderin these areas subjected to high loads and is therefore more durable inareas that are not subjected to such high thermal stress but remainssoft enough and retains its embedding capacity to fulfil tribologicalrequirements. The anti-friction coating automatically adapts in acertain way to the respective load state. Overall, this enables both thegalling resistance properties as well as the bearing capacity and wearresistance to be improved. Furthermore, the advantage of producing thealloy using a cold gas spraying process is that the substrate materialis subjected to only slight stress due to temperature, which means thateven temperature-sensitive substrates can be spray-coated with the alloyproposed by the invention or the anti-friction coating, without thesubstrate undergoing any change, for example in terms of mechanicalproperties. In addition, compared with other thermal spraying processes,thick coatings with a high coating quality can be produced, therebyenabling the best thickness coating to be selected for the individualapplication. As a result of the low temperatures, the resulting coatingsare low in oxides, which has a positive effect on many of the propertiesof the coating. Furthermore, the alloy or the coatings can be producedeasily and inexpensively due to simple processing and high coatingefficiency.

In one embodiment, the mean particle size of the dispersed soft phaseand/or hard phase is 1 μm to 100 μm, preferably 5 μm to 20 μm, whichensures an optimal mean particle size of the dispersed phases for therespective application and hence both a sufficient minimum size toguarantee effectiveness and a maximum size which does not impairmechanical strength.

Due to the fact that the range of the phase boundary in which the solidsolution or bond is formed has an average thickness in the range ofbetween 0.1 μm and 3 μm, preferably between 0.5 μm and 2.5 μm, asufficiently large grain is present in the alloy but has not yet formeda solid solution or bond with the matrix, which ensures that soft phaseswill still guarantee good galling resistance properties and hard phaseswill retain a high wear resistance.

The matrix element is selected from an element group comprisingaluminium, chromium, copper, magnesium, manganese, molybdenum, nickel,silicon, tin, titanium, tungsten and zinc, and the soft phase element isdifferent form the matrix element, the advantage of which is thatproperties of the alloy, such as temperature resistance and basicstrength, can be specifically adapted to the respective intended use andapplication, in addition to which the pricing of the bearing can beinfluenced to a certain degree.

In another embodiment, the proportion of matrix element is at least 55%by weight, in particular at least 65% by weight, the advantage of whichis that the anti-friction coating has a high mechanical strength and thesoft phases and/or hard phases can be optimally embedded in the matrix.

The soft phase may be at least one element selected from an elementgroup comprising silver, aluminium, gold, bismuth, carbon (graphite),calcium, copper, indium, magnesium, lead, palladium, platinum, scandium,tin, yttrium, zinc and lanthanoids, and the soft phase element isdifferent from the matrix element. This enables the tribologicalproperties of the alloy or anti-friction coating to be optimally adaptedto the specific application due to the different properties, inparticular the different degrees of hardness, of the different softphases and an optimal selection for an intended application can be madewith respect to temperature resistance, in particular coefficients ofdiffusion and the tendency to diffuse in conjunction with the matrixelement.

In one embodiment, the soft phase is selected from a group comprisingMoS₂, PTFE, Silicone, barium sulphate, and mixtures thereof, theadvantage of which is that the bearing element can also be used entirelywithout or with only the smallest quantities of lubricant, e.g. greaseor oil.

In another embodiment, the proportion of soft phase is in the range ofbetween 10% by weight and 45% by weight, in particular between 15% byweight and 35% by weight, the advantage of which is that the embeddingcapacity and galling resistance properties of the bearing can beadjusted to suit the respective application.

It is also of advantage if the hard phase is formed by at least oneelement selected from an element group comprising boron, carbon(diamond), cobalt, hafnium, iridium, molybdenum, niobium, osmium,rhenium, rhodium, ruthenium, silicon, tantalum, tungsten and zirconium,and the hard phase element is different from the matrix element, becausethe properties of the alloy in terms of strength and its wear resistanceand temperature resistance can be selected within a broad rangespecifically to suit the intended application.

In another variant, the hard phase is selected from a group comprisingZnS₂, BN, WS₂, carbides, such as for example SiC, WC, B₄C, oxides, suchas for example MgO, TiO₂, ZrO₂, Al₂O₃, and mixtures thereof, theadvantage of which is that high particle hardness levels and hence avery high wear resistance can be obtained.

In another embodiment, the proportion of hard phase is in the range ofbetween 3% by weight and 25% by weight, in particular between 5% byweight and 20% by weight, thereby enabling wear resistance to beoptimised.

In one embodiment of the composite material, an additional coating isformed between the first peripheral coating and the second peripheralcoating and constitutes a diffusion barrier or adhesion coating, theadvantage of which is that optimum adhesion or a diffusion barrier canbe obtained between the two coatings even when using different substratematerials for the second peripheral coating and different matrixelements for the anti-friction coating.

In one embodiment of the method, the second peripheral coating is formedby a supporting layer, for example made from steel, and the firstperipheral coating is sprayed on top of it, which increases strength andlengthens the service life of the bearing, for example, becausemechanical forces acting on the bearing can be absorbed or deflected bythe supporting layer.

It is also of advantage if an additional coating is provided in the formof a diffusion barrier or adhesion coating between the first peripheralcoating and the second peripheral coating and is sprayed on top of thesecond peripheral coating, because this enables the diffusion barrier oradhesion coating to be sprayed on first of all, after which the alloyproposed by the invention is sprayed on top of it, all in a continuousoperation using the same equipment, without having to manipulate thesupporting layer.

The process gas may be a gas selected from a group comprising helium,argon, nitrogen and mixtures thereof, thereby enabling high sprayingrates to be achieved as well as low oxidation of the initial powder.

The gas temperature may be selected from a range of between 60% and 95%of the melting temperature of the alloy element with the lowest meltingtemperature, the advantage of which is that a high adhesion and coatingquality of the join can be achieved depending on the alloy elementsused.

In one variant, the gas temperature is selected from a range of between65% and 90%, preferably between 70% and 85%, of the melting temperatureof the alloy element with the lowest melting temperature, which enablesthe amount of oxygen absorbed by the powder to be reduced and thusresults in a coating with a lower oxide content.

In another variant, the gas temperature may be selected from a range ofbetween 95% and 130% of the melting temperature of the alloy elementwith the lowest melting temperature, which enables the coating qualityto be further increased by raising the particle velocity, resulting inbetter adhesion of the particles, and the particles are prevented frombecoming totally molten due to the extremely short dwell time in the gasjet.

Due to the fact that a separate cold gas spray system is used for eachalloy element used and for each phase, the spraying parameters can beoptimised in the best possible way for each individual element, enablingan optimum coating quality to be obtained.

By virtue of another option, the initial powder used for sprayingpurposes has a particle diameter in the range of 3 μm to 70 μm,preferably 5 μm to 55 μm, as a result of which the mechanical propertiesof the anti-friction coating can be adapted to requirements within abroad range.

The invention further relates to the use of the alloy to produce ananti-friction coating of an anti-friction bearing or a thrust washer orfor directly coating components subjected to friction.

To provide a clearer understanding, the invention will be explained inmore detail with reference to the appended drawings. The schematicallysimplified diagrams illustrate the following:

FIG. 1 is a schematic diagram showing the structure of an anti-frictioncoating made from the alloy proposed by the invention;

FIG. 2 shows an anti-friction coating proposed by the invention appliedto a bearing element in the form of a bearing half-shell;

FIG. 3 illustrates the change in hardness of the anti-friction coatingin areas subjected to load during the operating time.

Firstly, it should be pointed out that the same parts described in thedifferent embodiments are denoted by the same reference numbers and thesame component names and the disclosures made throughout the descriptioncan be transposed in terms of meaning to same parts bearing the samereference numbers or same component names. Furthermore, the positionschosen for the purposes of the description, such as top, bottom, side,etc,. relate to the drawing specifically being described and can betransposed in terms of meaning to a new position when another positionis being described. Individual features or combinations of features fromthe different embodiments illustrated and described may be construed asindependent inventive solutions or solutions proposed by the inventionin their own right.

FIG. 1 provides a schematic diagram illustrating the structure 1 of ananti-friction coating made from the alloy proposed by the invention.

Particles or grains of a matrix alloy element and a matrix 2 areillustrated, as well as particles or grains of a soft phase 3. Theanti-friction coating or alloy produced by a cold gas spraying processconsists of alloy elements, the combination of which in thermodynamicequilibrium forms a non-separating alloy system.

It should be pointed out at this stage that in FIG. 1, the shape andsize of the individual grains or particles and the size ratio of thegrains relative to one another are not illustrated true to scale andthis is merely a schematic diagram.

A copper-tin anti-friction coating can be produced, in which, forexample, the matrix 2 or a matrix element is formed by copper and thesoft phase 3 or soft phase element is formed by tin, which imparts goodtribological properties to the anti-friction coating.

However, the corresponding phase diagram teaches that, for an assumedcomposition of approximately 75% by weight of copper and 25% by weightof tin (for the sake of simplicity, other additional alloying elementswhich are used to improve the properties of the anti-friction coatingare not addressed), the copper element will form inter-metallic phaseswith the tin element at these concentrations and the tin will dissolvein the α-copper phase and form mixed crystals.

The alloy or the structure schematically illustrated in FIG. 1 shouldtherefore not exhibit a copper matrix 2 and tin soft phases 3, butrather copper-rich α-mixed crystals and inter-metallic Cu—Sn phases.This material would not be very suitable for use as anti-frictioncoatings due to the absence of soft phases.

Due to the fact that the alloy proposed by the invention is produced bymeans of a cold gas spraying process, it is now possible to produce thetin soft phases 3 which are suitable for anti-friction coatings in thisnon-separating alloy system. As a result, the desired tribologicalproperties can also be achieved with the Cu, Sn combination of elementsand all the advantages which these elements offer in alloys foranti-friction coatings can expediently be used, such as highavailability, inexpensive raw material costs, ease of processing, goodmechanical properties.

The copper-tin alloy system is but one example of a whole range of othernon-separating alloy systems and the protective scope of the inventionis not restricted to this particular one. The person skilled in thisfield will be able to devise other element combinations within thespecified ranges on the basis of this teaching and these compositionsalso fall within the scope of the invention.

The formation of inter-metallic phases or mixed crystals between thematrix 2 and the soft phase 3 takes place within only a narrow region ofa phase boundary 4 of the matrix 2 with the soft phase 3. Thecomposition of the soft phase 3 remains in its original form. Theformation of the joint in the region of the phase boundary 4 naturallytakes place on the basis of a controlled diffusion.

The explanations given above with reference to FIG. 1 in respect of softphases 3 also applies to hard phases, in which case the alloy elementswhich would form mixed crystals or inter-metallic compounds with otherelements contained in the alloy based on the corresponding phase diagramform hard phases 5 and remain in their original composition. Theseelements are therefore able to unleash their full effect in improvingwear resistance and this property is therefore not partially lost as itwould otherwise be due to the formation of mixed crystals and is notreduced in any way.

The hard phases 5 are dispersed in the matrix 2, and the originalcomposition is maintained in the interior of the grain and a compound isformed only in the region of the phase boundary 4 with the matrix 2and/or with the soft phase 3.

The invention is not limited to systems based on two substances but alsolends itself to systems based on three or more substances because thesoft phase 3 and/or the hard phase 5 can already be formed with systemsbased on one or more substances.

The expression “non-separating” in this connection should be understoodas meaning that the element constituting the matrix 2 forms anon-separating alloy system with the main alloy element of the softphase 3 and/or the hard phase 5, for example in hot metallurgicalprocessing.

With regard to adding the elements forming the soft phase, theproperties of the anti-friction coating can be optimised insofar asmixtures adapted to the respective application in terms of the ductilityof the elements are produced, which, in addition to the desired gallingresistance properties, also have a higher mechanical strength to acertain extent.

For example, the soft phase 3 may be selected from a group comprisingMoS₂, PTFE, silicone, barium sulphate as well as mixtures thereof, as aresult of which anti-friction coatings with good anti-friction andgalling resistance properties can be produced which even permit dryoperation if necessary. This enables operation with a small amount oflubricant or no lubricant. Anti-friction coatings of this type are alsocharacterised by their low maintenance requirements.

The anti-friction coating proposed by the invention may also be producedby a galvanic process and may be reinforced with particles to improvethe mechanical properties.

FIG. 2 illustrates an anti-friction coating proposed by the inventiondisposed in an anti-friction element 6 in the form of a bearinghalf-shell.

The alloy or anti-friction coating proposed by the invention may beproduced by means of a cold gas spraying process at temperatures belowthe melting point of the element with the lowest melting point. However,the gas temperature may also be above this melting point because, due tothe short dwell time of the particles in the gas jet, the particles arenot fully melted. The high kinetic energy applied to the spray particlescauses a dense structure or a dense structure can occur when theparticles collide with a substrate 7 which may simultaneously serve as asupporting layer of the anti-friction element 6. To this end, however,the particles must exceed a velocity that is characteristic for therespective material.

To this end, a gas is accelerated to hypersonic speed in a Laval nozzle,for example. The coating material or the materials of the individualphases are injected into the gas jet as a powder in front of this nozzleand accelerated towards the substrate 7.

The basic structure of such a cold gas spraying system is known from theprior art and more details may be obtained by referring to patentspecification EP 0 484 533 B1 or WO 01/00331 A2, for example.

The substrate 7 may be provided in the form of a steel layer, forexample, which imparts high mechanical strength to the bearing. Inprinciple, however, any other material, in particular steels orlightweight metal alloys, would possibly suffice to satisfy requirementsin terms of mechanical and thermal strength.

It is of advantage that the substrate is subjected to only slightthermal stress due to the relatively low temperatures prevailing duringcold gas spraying and it is therefore possible to use lesstemperature-resistant materials for the substrate 7, which would not besuitable if using other thermal spraying processes due to the highstress caused by operating temperatures. As a result, allowance may bemade for individual requirements when producing an anti-frictionbearing, for example in terms of strength or resistance to corrosion.

It is also possible to apply extra heat to the gas jet, which willincrease the flow rate of the gas and hence also the particle velocity,thereby improving the properties of the coating in terms of its density,homogeneity or adhesion capacity in particular.

As illustrated in FIG. 2 in the form of a bearing half-shell, the alloyproposed by the invention may comprise a first peripheral coating 8which may be sprayed onto a second peripheral coating 9 or onto thesubstrate. However, the substrate 7 or the second peripheral coating 9does not have to be a half-shell and a full shell could be used as thesubstrate 7 or second peripheral coating by configuring or disposing thecold gas spraying system and the nozzles accordingly, in which case thefirst peripheral coating 8 can be sprayed on by an appropriate movementof the substrate 7 relative to the nozzle of the cold gas sprayingsystem.

For the purpose of the invention, an additional coating (not illustratedin FIG. 2) may be provided between the first peripheral coating 8 andthe second peripheral coating 9 in the form of a diffusion barrier or anadhesion coating, since this will improve the adhesion of theanti-friction coating, respectively the first peripheral coating 8, onthe second peripheral coating 9 or prevent a diffusion of elementsbetween the first and the second peripheral coating 8, 9, on the onehand. On the other hand, a multi-coat bearing can be produced withidentical equipment, essentially without having to change parts.

Due to the fact that the particles do not melt in the gas jet, coatingswith an extremely low oxide content can be produced and the oxygencontent of the coating is no higher than that of the particles in theinitial powder used to produce the coating.

It has proved to be of advantage if the equipment used for the cold gasspraying process is optimised so that, for example, a separate sprayingsystem is used respectively for the matrix 2 and the soft phase 3 and/orthe hard phase 5, which means that spraying parameters can be optimisedto suit the respective material used, for example pressure, temperatureor particle velocity.

This results in better adhesion of the particles to the substrate inparticular, thereby enabling the coating quality to be improved. Otheroptimisation possibilities for adapting to individual applications arethe spraying distance, the size of particles used, the process gas usedand the nozzle geometry used.

The process gas may be nitrogen, argon, neon, xenon or helium ormixtures thereof.

FIG. 3 illustrates the change in hardness of the anti-friction coatingin the areas subjected to stress during operation.

Due to the presence of the soft phase 3 or the hard phase 5 in thematrix 2 in its original composition and due to the fact that a bondforms only in the region of the phase boundary 4, the anti-frictioncoating or the anti-friction element 6 has particularly good propertieswith regard to adaptability, ability to embed foreign particles, goodgalling resistance properties and a high bearing capacity.

During operation with the anti-friction element 6, the temperature inareas of the anti-friction coating subjected to high loads is naturallyhigher than in areas subjected to less load. Since the coefficient ofdiffusion of the different elements depends in principle to a largedegree on temperature, increased diffusion occurs in these areas so thatthe structure of the anti-friction coating approaches the state ofequilibrium resulting in a structural change in the direction of theequilibrium phases.

Particularly in the region of the phase boundary 4, for example, a mixedcrystal or an inter-metallic compound can form between the matrix 2 andthe soft phase 3 and/or hard phase 5 due to the higher temperatureswhich occur there as a result of high mechanical stress. This leads toan increase in the hardness of the anti-friction coating in these highlystressed areas, making it more resistant.

The anti-friction coating or anti-friction element 6 advantageouslyadapts to the load state induced by the co-operating friction elementand operating requirements.

The increase in hardness is plotted in the diagram of FIG. 3, where theoperating time is plotted on the X-axis and the hardness of the stressedareas of the coating is plotted on the Y-axis. The curve of thisincrease in hardness may also have curvatures and need not necessarilybe linear.

During operation, a sort of equilibrium state is reached after a periodof time, after which no further increase in hardness to speak of isobserved.

One possible variant of the alloy proposed by the invention will bedescribed taking the example of producing a CuSn15 alloy.

The initial powders are spherical copper particles in a size range ofapproximately 5 to 25 μm and spherical tin particles in a size range ofup to approximately 45 μm. The process gas is nitrogen. The gastemperature is 200° C. The initial powders are injected into the gas jetin front of the nozzle in the appropriate ratio and accelerated towardsthe substrate at a gas pressure of 25 bar from a spraying distance of 30mm. Consequently, a dense and firmly adhering coating which is also lowin oxides forms on the substrate and comprises a copper matrix with tinparticles dispersed in it, thereby achieving good tribologicalproperties.

The embodiments described are intended to illustrate possible examplesof the alloy and the anti-friction element 6 and it should be pointedout at this stage that the invention is not restricted to theembodiments specifically described as examples here, and variouscombinations of the individual embodiments are also possible, in whichcase these possible embodiments are within the reach of the personskilled in this technical field using the teaching of the invention.Accordingly, all conceivable embodiments which can be obtained on thebasis of a combination of individual details taken from the embodimentsdescribed fall within the scope of the invention.

Finally, for the sake of good order, it should be pointed out that, inorder to provide a clearer understanding of the structure of theanti-friction coating and the anti-friction element 6, it and itsconstituent parts are illustrated to a certain extent out of scaleand/or on an enlarged scale and/or on a reduced scale.

The individual objectives and associated solutions may be found in thedescription.

Above all, the individual embodiments of the subject matter illustratedin FIGS. 1; 2; 3 may be construed as independent solutions proposed bythe invention in their own right. The underlying objectives andassociated solutions may be found in the detailed descriptions of thesedrawings.

LIST OF REFERENCE NUMBERS

-   1 Structure-   2 Matrix-   3 Soft phase-   4 Phase boundary-   5 Hard phase-   6 Anti-friction element-   7 Substrate-   8 Peripheral coating-   9 Peripheral coating

1. Alloy, in particular for an anti-friction coating, comprisingelements which form a matrix (2) and at least a soft phase (3) and/or ahard phase (5), which soft phase elements and/or hard phase elementsform a solid solution or a bond with the matrix element, wherein thesoft phase (3) and/or the hard phase (5) is dispersed in the matrix (2)and the solid solution or bond is formed only in the region of the phaseboundary (4) of the matrix (2) with the soft phase (3) and/or with thehard phase (5).
 2. Alloy as claimed in claim 1, wherein the meanparticle size of the dispersed soft phase (3) and/or hard phase (5) is 1μm to 100 μm, preferably 5 μm to 20 μm.
 3. Alloy as claimed in claim 1,wherein the region of the phase boundary (4) in which the solid solutionor bond is formed has an average thickness in the range of between 0.1μm and 3 μm, preferably between 0.5 μm and 2.5 μm.
 4. Alloy as claimedin claim 1, wherein the matrix element is selected from a groupcomprising aluminium, chromium, copper, magnesium, manganese,molybdenum, nickel, silicon, tin, titanium, tungsten and zinc, and thesoft phase element is different from the matrix element.
 5. Alloy asclaimed in claim 4, wherein the proportion of matrix element is at least55% by weight, in particular at least 65% by weight.
 6. Alloy as claimedin claim 1, wherein the soft phase (3) is at least one element selectedfrom an element group comprising silver, aluminium, gold, bismuth,carbon (graphite), calcium, copper, indium, magnesium, lead, palladium,platinum, scandium, tin, yttrium, zinc and lanthanoids, and the softphase element is different from the matrix element.
 7. Alloy as claimedin claim 1, wherein the soft phase (3) is selected from a groupcomprising MoS₂, PTFE, silicone, barium sulphate and mixtures thereof.8. Alloy as claimed in claim 6, wherein the proportion of soft phase isin the range of between 10% by weight and 45% by weight, in particularbetween 15% by weight and 35% by weight.
 9. Alloy as claimed in claim 1,wherein the hard phase (5) is at least one element selected from anelement group comprising boron, carbon (diamond), cobalt, hafnium,iridium, molybdenum, niobium, osmium, rhenium, rhodium, ruthenium,silicon, tantalum, tungsten and zirconium, and the hard phase element isdifferent from the matrix element.
 10. Alloy as claimed in claim 1,wherein the hard phase (5) is selected from a group comprising ZnS₂, BN,WS₂, carbides such as for example SiC, WC, B₄C, oxides, such as forexample MgO, TiO₂, ZrO₂, Al₂O₃, and mixtures thereof.
 11. Alloy asclaimed in claim 9, wherein the proportion of hard phase is in the rangeof between 3% by weight and 25% by weight, in particular between 5% byweight and 20% by weight.
 12. Anti-friction coating, in particular abearing anti-friction coating, made from an alloy, wherein the alloy isas claimed in claim
 1. 13. Composite material comprising at least afirst peripheral coating (8) and a second peripheral coating (9)disposed on top of it, for example a supporting layer made from steel,in particular for anti-friction bearings or thrust washers, wherein thefirst peripheral coating (8) is formed by an anti-friction coating asclaimed in claim
 12. 14. Composite material as claimed in claim 13,wherein an additional coating is provided between the first peripheralcoating (8) and the second peripheral coating (9) in the form of adiffusion barrier or adhesion coating.
 15. Method of producing acomposite material comprising at least a first peripheral coating (8)and a second peripheral coating (9) disposed on top of it, in particularfor anti-friction bearings or thrust washers, wherein an alloy asclaimed in claim 1 is produced as a first peripheral coating (8) bymeans of a cold gas spraying process.
 16. Method as claimed in claim 15,wherein the second peripheral coating (9) is formed by a supportinglayer, made from steel for example, and the first peripheral coating (8)is sprayed on top of it.
 17. Method as claimed in claim 15, wherein anadditional coating is provided between the first peripheral coating (8)and the second peripheral coating (9) in the form of a diffusion barrieror adhesion coating and it is sprayed on top of the second peripheralcoating (9).
 18. Method as claimed in claim 15, wherein the process gasis selected from a group comprising helium, argon, nitrogen, andmixtures thereof.
 19. Method as claimed in claim 18, wherein the gastemperature is selected from a range of between 60% and 95% of themelting temperature of the alloy element with the lowest meltingtemperature.
 20. Method as claimed in claim 18, wherein the gastemperature is selected from a range of between 65% and 90%, preferablybetween 70% and 85%, of the melting temperature of the alloy elementwith the lowest melting temperature.
 21. Method as claimed in claim 18,wherein the gas temperature is selected from a range of between 95% and130% of the melting temperature of the alloy element with the lowestmelting temperature.
 22. Method as claimed in claim 15, wherein aseparate cold gas spraying system is provided for each alloy elementused and for each phase.
 23. Method as claimed in claim 15, wherein theinitial powder used for spraying has a particle diameter in the range offrom 3 μm to 70 μm, preferably from 5 μm to 55 μm.
 24. Use of the alloyas claimed in claim 1 to produce an anti-friction coating of ananti-friction bearing.
 25. Use of the alloy as claimed in claim 1 toproduce a thrust washer.
 26. Use of the alloy as claimed in claim 1 toproduce directly coated bearing components, for example cans.